1. Field of the Invention
This invention relates to a method for fabricating a thin film magnetic head, and particularly to a method for milling a writing magnetic pole portion of the thin film magnetic head.
2. Related Art Statement
A writing magnetic pole portion of a writing element constituting a thin film magnetic head is fabricated as follows. First of all, a first magnetic film functioning as a bottom magnetic layer of the writing element is formed and then, a second magnetic film functioning as a top magnetic layer of the writing element is formed by means of a frame-plating method. Then, the thus obtained multilayered structure is ion-milled, to fabricate the writing magnetic pole portion.
FIGS. 1 and 2 an elevational views showing a thin film magnetic head fabricated on a wafer as is viewed from the air bearing surface (ABS). FIG. 3 is a cross sectional view of the thin film magnetic head illustrated in FIG. 1, taken on line A—A. The above ion-milling process includes an ion-milling process in the depth direction and an ion-milling process in the width direction. In the ion-milling process of depth direction, as shown in FIG. 1, the first magnetic film 1 is dry-etched in the depth direction D by utilizing the second magnetic film 3 as a mask so that the width of the portion 1A of the first magnetic film 1 opposite to the second magnetic film 3 is set equal to the width of the second magnetic film 3. In the ion-milling process of width direction, the first magnetic film 1 and the second magnetic film 3 are dry-etched in the width direction W and thus, reduced in width, to define the width of the writing magnetic pole portion 10.
A MR element 65 is formed below the first magnetic film 1 and above a base 61 made of AlTiC via a base underlayer 62 and a bottom shielding film 63. Reference numeral “2” designates a gap layer and reference numeral “67” designates a coil film which is embedded in an insulating film 66.
FIG. 4 is an enlarged view showing a portion of a wafer where thin film magnetic heads are fabricated. In FIG. 4, attention is paid to one of the thin film magnetic heads. The above-mentioned ion-milling of depth direction and of width direction are performed by irradiating ion beam 5 at a given angle on the wafer with rotating the wafer continuously around the center O of the wafer in the direction parallel to the wafer surface. Hereinafter, the rotation may be called as “dynamic rotation”. In addition, the width of the writing magnetic pole portion is set to 0.6 μm or below, recently.
In this case, the width of the writing magnetic pole portion 10 may be changed in the direction parallel to the Throat Height (TH) due to shadow effect which is originated from the steps of the second magnetic film 3 and the insulating layer 6. Therefore, the widths of the writing magnetic pole portions may be changed on every wafer and even on the same wafer. As a result, the yield ratio in fabrication of the thin film magnetic film may be decreased.
The fluctuation in width of the writing magnetic pole portions becomes remarkable at the forefronts of the magnetic pole portions, so that the absolute sizes of the magnetic pole portions are largely fluctuated if the Throat Height (TH) length of the magnetic pole portion is set to 0.5 μm or below. In this case, therefore, the yield ratio in fabrication of the thin film magnetic head may be much decreased.